JSFiddle - React, Tailwind, and code Playground

HTML

<div id=d1></div>
<div id=d2>
  <div id="inner"></div>
</div>

CSS

div{
  width: 100px;
  height: 100px;
  margin-top: 10px;
}
#d1{
  background-color: black;
  opacity: .4;
}
#d2{
  opacity: .8;
}
#inner{
  width: 100%;
  height: 100%;
  background: black;
  opacity: .5;
}